a) FIELD OF THE INVENTION
The present invention relates to a method of physical and chemical pre-treatments of peat to be used in biofilters for wastewater treatment. These peat-based biofilters are suitable for domestic, industrial or urban applications. More particularly, the invention relates to a mixture of peat which has been pre-treated physically and then mixed with pre-determined concentrations of a) a Fe-containing compound, and b) lime. Also, this invention relates to a biofilter which utilises this pre-seived peat mixture for wastewater treatment.
b) BRIEF DESCRIPTION OF THE PRIOR ART
In recent years, there has been increasing interest in the incorporation of peat into wastewater treatment systems. Peat removes pollutants and microbial activity from wastewaters by adsorption and absorption reactions (Tihn et al., 1971, Can. Min. Metall. Bull, Vol, 64, pp.99-104). Peat has been demonstrated to be effective in the removal of suspended solids, macronutrients (nitrogen and phosphorus), heavy metals, trace organics, and fecal coliforms in a variety of situations. Case studies reported include the application of peat to treat domestic and industrial wastewater in both natural peatlands and constructed peat systems (Sarakka and Kamppi, 1971, Suo, Vol. 22, pp.51-58; Coupal and Lalancette, 1976, Water res., Vol. 10. pp.1071-1076; Gustenpergen, 1980, Can. J. of Chem. Eng, Vol 58, pp.235-240; Dubuc et al., 1986, Water Res. Bull., Vol. 22, pp.297-303).
Because of its low cost, coupled with is natural characteristics of absorption and adsorption, and its capacity to provide a favorable environment for microorganisms, peat offers great potential for the biological filtration of wastewater. Indeed, although several investigations have shown that peat is an effective medium for use in water pollution control, studies on treatment capacity of different types of peat are still very limited. A problem often met is the color-leaching of peat resulting in a yellow-brown color of water (Rock et al., 1984, J. Environ. Qual., Vol. 13, pp.518-523). Although leaching decreases with time (Rock et al., supra; Rana and Viraraghavan, 1987, Water Poll. Res. J. Canada, Vol.22, pp.491-504), colored discharges may affect the aesthetics of the effluent of the system.
Moreover, in some biofiltration systems internal clogging happens after a few days of operation (Buelna et al., 1989, Peat and Peatlands, Diversification and Innovations, Symposium of International scope on 8 themes of future applications of peat; August 6-10, Quebec City, Canada). The clogging is caused by small particles present in the peat bed which are found in the peat in amounts proportional to the humification degree of the peat. As a direct result of internal clogging problems, the hydraulic charge that may be applied daily to such a system is greatly restricted (0.04 to 0.2 m/day) (Brooks et al., 1984, J. Environ. Qual., Vol.13,(4), pp.524-530), therefore, diminishing the efficiency of such biofilters to very limited applications.
Also, consistent and efficient elimination of the phosphorus has not been achieved to date. Farnham and Brown (supra) have disclosed a system in which 99% of the total P was eliminated. However, these results were obtained with a system performing with hydraulic charges ranging from 0.1 to 0.2 m/day. These charges could hardly suffice to handle the demands of small municipalities or even domestic systems.
Still, in this respect Nichols and Boelter (1982, J. Env. Qual., Vol.11 (1), pp.86-92) disclosed a peat-sand filter bed which removes phosphorus in an efficient manner. However, these results were unreproducible after repeated efforts from other investigators.